diff --git a/src/schema.test.ts b/src/schema.test.ts
index c6b577de..66809c53 100644
--- a/src/schema.test.ts
+++ b/src/schema.test.ts
@@ -1,6 +1,6 @@
 import { assertEquals } from '@std/assert';
 
-import { percentageSchema } from '@/schema.ts';
+import { percentageSchema, sizesSchema } from '@/schema.ts';
 
 Deno.test('Value is any percentage from 1 to 100', () => {
   assertEquals(percentageSchema.safeParse('latvia' as unknown).success, false);
@@ -20,3 +20,12 @@ Deno.test('Value is any percentage from 1 to 100', () => {
 
   assertEquals(percentageSchema.safeParse('1e1').success, true);
 });
+
+Deno.test('Size or sizes has correct format', () => {
+  assertEquals(sizesSchema.safeParse('orphan' as unknown).success, false);
+  assertEquals(sizesSchema.safeParse('0000x 20x20' as unknown).success, false);
+  assertEquals(sizesSchema.safeParse('0000x10 20X20 1x22' as unknown).success, false);
+  assertEquals(sizesSchema.safeParse('1000x10 20X20 1x22' as unknown).success, true);
+  assertEquals(sizesSchema.safeParse('3333X6666 1x22 f' as unknown).success, false);
+  assertEquals(sizesSchema.safeParse('11xxxxxxx0 20X20 1x22' as unknown).success, false);
+});
diff --git a/src/schema.ts b/src/schema.ts
index a9dd56e3..23e2938d 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -65,6 +65,9 @@ const localeSchema = z.string().transform<Intl.Locale>((val, ctx) => {
   }
 });
 
+/** White-space separated list of sizes, each in the format <number with up to 4 digits>x<number with up to 4 digits> or with "X" in upper case. */
+const sizesSchema = z.string().regex(/^(?:[1-9]\d{0,3}[xX][1-9]\d{0,3})(?:\s+[1-9]\d{0,3}[xX][1-9]\d{0,3})*$/);
+
 export {
   booleanParamSchema,
   decode64Schema,
@@ -75,4 +78,5 @@ export {
   localeSchema,
   percentageSchema,
   safeUrlSchema,
+  sizesSchema,
 };